Lots of folks on here use PGRs to control plant growth. Generally we go with the generic brands which tend to be much cheaper. And yes, one use is to apply before over-seeding to keep the existing turf from towering over the seedlings too much. How much depends on your turf type. The label goes in great detail in this regards. 0.5oz/1000 is a good starting point for TTTF, for ex. Verify w the label regarding your turf.

 

What growth regulator do you use? I have been looking at T-Nex but it is a $136, and you get a ton of it. I just want something for my 5,000 sqft lawn.

 

Great thank you.. I have a tenacity syringe could I use it to measure the PGR ? if so approximately how much would 0.5oz be on the syringe. Thank you

 

Syringes work for small volumetric measurements, of course, but don’t omit to cleanup afterwards. They’ll dry & bind up otherwise. Personally I use a measuring cup. Easy to use, easy to clean.

 

Sounds good last question how often can I apply 0.05 oz thanks

 

Please read the label and verify what you need based on the directions.

If you apply a PGR, it is fine to do it before and during overseeding, but not once germination and sprouts happen. You should wait until the grass can be mowed 2-4+ times before considering resuming PGR. Some labels indicate to wait until next season.

How often:
*** Edit/Updated [Start]
The below example is for very short bentgrass. The application rate (per the PGR label) is different for various grasses, and it should be noted that longer/taller grass may have an effect on the optimal GDD. In studies against KBG, the GDD for re-application may have reached 300. The official product documentation does not specify GDD; but instead recommends anywhere from 1-4 weeks for re-application (at lower does for more often). I have posted GDD information as studies have found it to be more accurate and a better way to measure re-application timing.

*** Edit/Updated [End]

If you want maximum performance, you will use Growing Degree Days in Celsius. For Primo Maxx, the optimal value is 230. Use a calculator online from the day you put it down and when you hit 230, re-apply. You might be able to extend this to 300 GDD but has not been tested as optimal. Depending on the area and time of year/daylight/temperatures, this could be anywhere from 2 - 4 weeks on average. The recommended GDD is the time when the PGR is most effective and then starts to lose its effectiveness. After the 230 GDD (Primo Maxx), the plant growth will start to speed up and then eventually accelerate growth faster than normal growth (quickly using those suppressed plant hormones).

GDD is easily calculated. Search for a web site or service or app that does it for you. Here is how you do it yourself.

Take the day's low and high temperatures and average them. Then subtract your base temperature (when the plant doesn't grow) which for cool season is 0 degrees C.
An example in my area, on 4/6, I apply PGR. The high was 28 degrees C and the low was 16 degrees C. Add them up and divide in half to get an average of 22 degrees. Subtract 0 degrees and I get 22 - This is my GDD for the day. The next day the high/low was 11 and 6 - GDD is 8.5. If I add 22 + 8.5, I get 30.5. I would keep adding until I get to 230... then I know to re-apply the PGR.

If the temperature average is equal to or lower than the base temperature (0 degrees C), then we can say there is 0 growth for that day and the GDD is 0.
In my area,
Jan 1 - Jan 31 was 234 GDD.
Feb 1 - Feb 27 was 232 GDD.
Feb 28 - Mar 25 was 226 GDD.

As temperatures rise, the GDD each day increase, so
March 26 - Apri 9 was 184.5 GDD. I will likely hit 230 GDD sooner than ~ 1 months' time.

 

Please read the label and verify what you need based on the directions.

If you apply a PGR, it is fine to do it before and during overseeding, but not once germination and sprouts happen. You should wait until the grass can be mowed 2-4+ times before considering resuming PGR. Some labels indicate to wait until next season.

How often:
If you want maximum performance, you will use Growing Degree Days in Celsius. For Primo Maxx, the optimal value is 230. Use a calculator online from the day you put it down and when you hit 230, re-apply. You might be able to extend this to 300 GDD but has not been tested as optimal. Depending on the area and time of year/daylight/temperatures, this could be anywhere from 2 - 4 weeks on average. The recommended GDD is the time when the PGR is most effective and then starts to lose its effectiveness. After the 230 GDD (Primo Maxx), the plant growth will start to speed up and then eventually accelerate growth faster than normal growth (quickly using those suppressed plant hormones).

View attachment 9391


GDD is easily calculated. Search for a web site or service or app that does it for you. Here is how you do it yourself.

Take the day's low and high temperatures and average them. Then subtract your base temperature (when the plant doesn't grow) which for cool season is 0 degrees C.
An example in my area, on 4/6, I apply PGR. The high was 28 degrees C and the low was 16 degrees C. Add them up and divide in half to get an average of 22 degrees. Subtract 0 degrees and I get 22 - This is my GDD for the day. The next day the high/low was 11 and 6 - GDD is 8.5. If I add 22 + 8.5, I get 30.5. I would keep adding until I get to 230... then I know to re-apply the PGR.

If the temperature average is equal to or lower than the base temperature (0 degrees C), then we can say there is 0 growth for that day and the GDD is 0.
In my area,
Jan 1 - Jan 31 was 234 GDD.
Feb 1 - Feb 27 was 232 GDD.
Feb 28 - Mar 25 was 226 GDD.

As temperatures rise, the GDD each day increase, so
March 26 - Apri 9 was 184.5 GDD. I will likely hit 230 GDD sooner than ~ 1 months' time.

Does the 0 degree floor work for anywhere in the northeast? What would be the difference using 32 vs 0 degrees? I would assume 32 would stop growth as well? Im not debating, just curious because I’d like to keep track of my GDD this year

 

Very cool explanation. I thank you for it.

 

@LawnNub - I use the generic T-Nex. I've only bought the larger 2.5g jugs which used to offer a better value but lately these prices have gotten all out of whack and it's sometimes cheaper to buy the gallon. From a cost per 1000 perspective it's just about 50 cents/1000. While Anuew may have other advantages (a gentler ramp-up and ramp-down period, for ex) it's still not as cheap, per application, as TNex (1.5# of Anuew rings up for $120, and at the 0.18oz/1000 low rate it comes out to almost $1/1000).
Check out the Marketplace where we split these larger purchases amongst ourselves. Here's one: https://www.thelawnforum.com/thread...threads/tnex-pgr-plant-growth-regulator-8oz-in-bettix-bottle.43673/#post-561357

 

@Scagfreedom48z+

0 degree base is easier to deal with because you add the average temp up every single day. All temps are above 0. If using 32, you have to remember to only add up temps that are above 32 (or is it 32 and above? See...hard to remember sometimes).

The thing is, to do base 0, you have to use degrees C.

I just look up temps using wunderground's calendar feature, set to degrees C, and add them all up. Works for me.

 

I like this one:
Growing Degree Days | GreenCast | Syngenta

 

There is a long thread on PGR on cool season lawns here: PGR + Cool Season Grass

Amount to use depends on your HOC. I suggest keeping a control section in a corner of your property (an area without any PGR), so you can test the amount of suppression you get. Too much can cause problems too, more so during a humid summer days.

 

I have not reviewed the research in detail recently. Was there any discussion on the HoC affecting efficacy because of foliar application? As in did HoC only matter because more active ingredient was absorbed? Any working theories or guesses on the “why” HoC matters or not?

 

Lot of conflicting info on whether HOC or rate of T-Nex is a bigger factor in longevity of suppression. What I found, was that 280 GDD always seemed to be a sweet spot--and I was using rates between 0.25 and 0.50 oz (the rate range I found I preferred, personally) on 3.5-4.5 inch Fescue/KBG, etc. Not sure how many people that helps, since it's a specific set of conditions.

As to factors why HOC might matter, dunno. Maybe amount of photosynthesizing material. Maybe root to shoot ratio influences hormone responses or base production levels...we would have to get a molecular plant biologist to do some more experiments.

 

Kreuser himself states that
If you have a sweet spot, go with it. Not saying your wrong. Lot of factors go into duration of suppression and the amount of suppression but the two largest are rate used and hoc.

Increasing rate of pgr does not increase the longevity of the product as much so as it increases the amount of suppression straight from Kreuser. I.e. increasing the rate of primo on fairway height bentgrass from 11oz/A to 33oz/A increases suppression by 25% but only increases gdd from 350 to 380.